The 60 GHz band is an unlicensed band which features a large amount of bandwidth and a large worldwide overlap. The large bandwidth means that a very high volume of information can be transmitted wirelessly. As a result, multiple applications, each requiring transmission of large amounts of data, can be developed to allow wireless communication around the 60 GHz band. Examples for such applications include, but are not limited to, wireless high definition TV (HDTV), wireless docking stations, wireless Gigabit Ethernet, and many others.
In order to facilitate such applications, there is a need to develop integrated circuits (ICs) such as amplifiers, mixers, radio frequency (RF) analog circuits, and active antennas that operate in the 60 GHz frequency range. An RF system typically comprises active and passive modules. The active modules (e.g., a phased array antenna) require control and power signals for their operation, which are not required by passive modules (e.g., filters). The various modules are fabricated and packaged as radio frequency integrated circuits (RFICs) that can be assembled on a printed circuit board (PCB). The size of the RFIC package may range from several to a few hundred square millimeters.
In the consumer electronics market, the design of electronic devices, and thus RF modules integrated therein, should meet be designed to minimize cost, size, power consumption, and weight. The design of the RF modules should also take into consideration the current assembled configuration of electronic devices and, particularly, handheld devices such as laptop, smartphones, and tablet computers, in order to enable efficient transmission and reception of millimeter wave signals. Furthermore, the design of the RF module should account for minimal power loss of receive and transmit RF signals as well as for maximum radio coverage.
A schematic diagram of a RF module 100 designed for transmission and reception of millimeter wave signals is shown in FIG. 1. The RF module 100 includes an array of active antennas 110-1 through 110-N connected to a RF circuitry or IC 120. Each of the active antennas 110-1 through 110-N may operate as a transmit (TX) and/or a receive (RX) antenna. An active antenna can be controlled to receive/transmit radio signals in a certain direction, to perform beam forming, and to switch between receive and transmit modes. For example, an active antenna may be a phased array antenna in which each radiating element can be controlled individually to enable the usage of beam-forming techniques.
In the transmit mode, the RF circuitry 120 typically performs up-conversion, using a mixer (not shown in FIG. 1), to convert intermediate frequency (IF) signals to radio frequency (RF) signals. Then, the RF circuitry 120 transmits the RF signals through the TX antenna according to the control signal. In the receive mode, the RF circuitry 120 typically receives RF signals through the active RX antenna and performs down-conversion, using a mixer, to IF signals using the local oscillator (LO) signals, and sends the IF signals to a baseband module (not shown in FIG. 1).
In both receive and transmit modes, the operation of the RF circuitry 120 is controlled by the baseband module using a control signal. The control signal is utilized for functions such as gain control, RX/TX switching, power level control, beam steering operations, and so on. In certain configurations, the baseband module also generates the LO and power signals and transfers such signals to the RF circuitry 120. The power signals are DC voltage signals that power the various components of the RF circuitry 120. Normally, the IF signals are also transferred between the baseband module and the RF circuitry 120.
In common design techniques, the array of active antennas 110-1 to 110-N are implemented on the substrate upon which the IC of the RF circuitry 120 is also mounted. An IC is typically fabricated on a multi-layer substrate and metal vias that connect between the various layers. The multi-layer substrate may be a combination of metal and dielectric layers and can be made of materials such as a laminate (e.g., FR4 glass epoxy, Bismaleimide-Triazine), ceramic (e.g., low temperature co-fired ceramic LTCC), polymer (e.g., polyimide), PTFE (Polytetrafluoroethylene) based compositions (e.g., PTFE/Ceramic, PTFE/Woven glass fiber), Woven glass reinforced materials (e.g., woven glass reinforced resin), wafer level packaging, and other packaging, technologies and materials. The cost of the multi-layer substrate is a function of the area of the layer—the greater the area of the layer, the greater the cost of the substrate.
Antenna elements of the array of active antennas 110-1 to 110-N are typically implemented by having metal patterns in a multilayer substrate. Each antenna element can utilize several substrate layers. In conventional implementations for millimeter wave communications, antenna elements are designed to occupy a single side of the multi-layer substrate side. This is performed in order to allow the antenna radiation to properly propagate.
For example, a millimeter wave (mm-wave) RF module 200 depicted in FIG. 2 includes a multi-layer substrate 210 and a plurality of antenna elements 220 implemented on an upper layer of the substrate 210. The antenna elements 220 are connected to a RF circuitry 230 using traces 201. The RF circuitry 230 performs the function discussed in greater detail above. The RF module 200 may also contain discrete electronic components 240 such as an antenna interface in an implementation of chip-board transition structure, which typically includes the IC (chip) package and transmission lines from the IC to the substrate. Additionally, circuits designed for impedance matching and electrostatic discharge (ESD) protection may also be part of the antenna interface.
In order to maximize the coverage of a millimeter wave RF module, the RF module operates according to the specification of the IEEE 802.11ad (also known as the WiGig), such that a large number of antennas should be included in the RF module. Some conventional RF designs require implementing a number of active antennas on one side of the substrate, thereby providing a constraint that limits the number of antennas of the RF module. Another conventional design includes placing a number of antennas on different sides of the substrate, thereby enabling the RF signal to radiate in all directions.
In both of the above noted approaches, an attempt to increase the number of active antennas would require increasing the area of substrate. Also, such an attempt would require increasing the length of the wires (traces) from the RF circuitry to the antenna elements. Further, some antennas require differential signal feeding via, e.g., a balun structure which consumes substrate area. In this case, a problem arises as some area of the substrate should be reserved for other structures, such as antenna feed lines. Any design of a RF module designed with a large number of antennas should meet the constraints of an efficient design. Such constraints necessitate that the physical dimensions, power consumption, heat transfer, and cost be minimized whenever possible.
Typically, the antennas that require differential signal feeding via, e.g., a balun structure, are dipole and Yagi-types antennas. More specifically, a dipole antenna is typically fed by two arms that are 180° out of phase with respect to each other. The arms must have equal electric field amplitude distribution. When a dipole is fed from an unbalanced source (unequal field distribution), such as a coax or microstrip, a balun is used to transition the source transmission line from an unbalanced state to a balanced state. The balanced transmission line is generally in the form of a two-wire line.
Additionally, when fed over a ground plane, a dipole antenna needs to be on the order of a quarter-wavelength from the ground so that the dipole is not shorted to the ground plane.
In existing solutions, the feed line from the ground to the dipole is typically designed using a balanced line. The balun is implemented in an earlier stage of the antenna as a separate component. This requires more space and line length, which are disadvantages in a system that is space limited. Other solutions use the quarter wavelength section from the ground as a matching section and part of the balun. However, this type of balun cannot support a broadband frequency range.
Another design constraint that should be considered when providing an RF module with a large number of millimeter-wave antennas is the connection of an antenna to multiple amplifiers for increased transmission power and/or reception sensitivity. Typically, such a connection requires an extra circuit element: a power combiner. The power combiner can be in the form of a simple T-junction or a more complex Wilkinson divider. In either case, extra line length and circuitry must be added for the combiner and any associated matching network. As a result, a problem arises with such designs as the area of the substrate is limited and should be reserved for other structures. Thus, an attempt to increase the number of antennas in a mm-wave RF module while meeting the above-noted constraints would significantly increase the area of the module's substrate and, therefore, reduce the efficiency of the RF module.
It would be therefore advantageous to provide an efficient design for mm-wave antennas that overcomes the disadvantages noted above.